1. Field of the Invention
The present invention relates to a sensor for use in signalling when a patient falls out of or otherwise leaves a bed against the wishes of a caregiver. The sensor is also useful in signalling when a patient who is lying on a mattress overlay product such as foam or an air cushion contacts the mattress surface underneath the overlay product.
2. Description of the Prior Art
There is a need for effective signalling of a caregiver when a patient, who is likely to suffer injury by leaving his bed without assistance, falls or gets out of bed. There is also a need for effective signalling of a caregiver when a patient, who is lying upon a mattress overlay to reduce tissue interface pressure and in turn prevent or treat pressure ulcers, bottoms upon the mattress; that is, when part of the patient such as a bony prominence, contacts the mattress surface beneath the overlay product.
Various patient monitors are known in the prior art. For example, U.S. Pat. No. 4,020,482 to Feldl relates to a patient monitor including an elongated air inflated flexible bag placed below a mattress and connected to a pressure actuated electrical switch at a remote station. The switch is a normally closed low pressure switch which remains open as long as a patient's weight is on the mattress and closes when the patient's weight is removed. In essence, removal of the weight lowers the pressure in the bag which closes the switch. U.S. Pat. No. 3,533,095 to Collins is of interest in that an air mattress is provided upon which an animal is placed in a first position. For example, a mare is placed upon the mattress in a standing position. When the mare lies down the displacement of her weight causes air from the mattress to expand into a connection to a normally open pressure switch, thereby closing the switch and activating an alarm.
U.S. Pat. No. 3,781,843 to Harrison et al. is of interest in that pressurized fluid is contained in members having a fluid filled passageway which can be attached to the side rails, etc. of a bed. When someone gets out of the bed he typically will grasp such rails and activate an alarm. U.S. Pat. No. 4,175,263 to Triplett et al. is of interest in that it relates to a plurality of pressure sensors.
U.S. patents of general interest which relate to electrical switches which are directly activated by contacts which close under the weight of a patient and open when such weight is removed include the following:
______________________________________ 4,228,426 Roberts 4,242,672 Gault 4,638,307 Swartout 4,700,180 Vance ______________________________________
The use of a sensor relying upon a fluid such as air under pressure is highly desirable. However, known sensors of this type are subject to leakage or rupture of a sealed bladder. It is an object of the present invention to provide a sensor which is responsive to changes in the fluid pressure of a constantly supplied fluid to signal an out of bed condition or a bottoming condition or both but which is not prone to leakage or rupture.
It is also an object of the present invention to provide such a sensor which will allow the use of multiple resilient means having a fluid continuously supplied under pressure thereto.
Another object of the present invention is to provide such a sensor which will allow a caregiver at a remote location to readily determine whether a patient is in or out of a bed.
A further object of the present invention is to provide such a sensor which will allow a caregiver at a remote location to readily determine whether a patient has bottomed when lying on a mattress overlay device.
Yet another object of the present invention is to provide such a sensor which will allow a caregiver at a remote location to readily determine the position of a patient relative to the surface upon which the patient is lying.